It is well-known that metals such as, for example, nickel and iron can be recovered from reduced metal-containing mixtures, using carbonylation processes. Volatile nickel and iron carbonyls are formed at elevated temperatures and pressures, separated, isolated and thermally decomposed to yield pure metal pellets and carbon monoxide gas. The purity of the nickel metal produced by this process is extremely high because of the selectivity of the carbonylation reaction and the fact that the other metals, often present with nickel, are either easily separated, or do not form gaseous compounds. However, in contrast, iron carbonyl cannot be completely separated from nickel carbonyl because these compounds form an inseparable isotropic mixture.
It has been reported that cobalt, which is often present with nickel and iron in metal-containing mixtures, such as ores and tailings, together forms a cobalt carbonyl under similar conditions particularly, when hydrogen is used, together with carbon monoxide for the formation of carbonyls. Cobalt carbonyl, having much lower vapour pressure than nickel and iron carbonyls, usually remains in the carbonyl reactor together with solid leftovers of the carbonylation reaction, or is partially carried, together with volatile carbonyls, and left as a solid residue after nickel and iron carbonyls' fractional separation. The further isolation of cobalt usually involves desolution of cobalt in acid, followed by electrowinning.
Similarly, carbonylation of metals-containing mixture as in alkaline solution leads to the formation of gaseous nickel carbonyl as well as iron and cobalt carbonyl compounds that remain the solution. A further refining of cobalt involves an acidification of the solution, followed by cobalt organic solvent extraction. The extracted cobalt is then purified by electrowinning.
There have been several attempts to achieve cobalt extraction using volatile cobalt carbonyl precursors such as cobalt hydrocarbonyl. For example, when a slurry of cobalt, nickel and copper metals were treated with a carbon monoxide-hydrogen gas mixture at 68 bar pressure, mixtures of nickel carbonyl and cobalt carbonyl anions were produced. Volatile nickel carbonyl was degassed from the solution and the residue was filtered out. The basic solution of cobalt carbonyl salt was acidified with strong acid and volatile cobalt hydrocarbonyl boiled and removed from solution. Subsequent decomposition of cobalt hydrocarbonyl resulted in a pure cobalt metal containing 30 ppm of Ni, 0.4 ppm of Fe and 0.1 ppm of copper. This procedure involves several handling processes, including filtration of the solution, dilution and acidification of the resulting solution.
Other separations of cobalt carbonyl from nickel carbonyl involved addition of ammonia to precipitate {Co(NH3)6ΠCo (CO)4]2, or cobalt removal by passage through ethanolic KOH.
It is known that iron nitrosyl carbonyl Fe(NO)2(CO)2 has been prepared in the gaseous state by the reaction of NO with FE(CO)5 at 95° C., and in aqueous alkaline solution. However, I have discovered that CoNO(CO)3 can be beneficiously and efficaciously distilled from Fe-containing carbonyl species to provide Fe-free CoNO(CO)3 gas for subsequent decomposition to pure cobalt metal (99.8%).